The invention relates generally to a method and apparatus for monitoring environmental conditions, and more particularly to a method and apparatus for determining whether an object has been exposed to a temperature that has exceeded a predetermined threshold.
There are many circumstances where it may be desirable to monitor, control, and record the environmental parameters of a given environment. For example, the quality and safety of pharmaceuticals, food products, chemicals, and biological products can be adversely affected by improper temperature control during processing, distribution, and storage.
A number of different devices have been developed to monitor and record changes in temperature over a period of time. Time-Temperature Indicators (TTI) are devices that can be used for monitoring the time-temperature history of various products. TTI devices generally use a change in physical appearance to indicate temperature exposure. Electronic monitoring devices are a second type of device that may be used to monitor temperature exposure. Electronic monitoring devices are typically small portable devices that include instruments and memory for measuring and storing temperature readings.
TTIs typically use mechanical, chemical, electrochemical, enzymatic, or microbiological change that may be expressed as a visible response in the form of a mechanical deformation, color development, or color movement. The rate of change can be temperature dependent so that it increases at higher temperatures. As a result, the physical response may be used to give a cumulative indication of the temperature conditions to which the TTI has been exposed. TTI devices can usually be activated in a variety of ways, such as removing from very cold storage, mixing two liquids together or bringing two layers into contact. Typically, these TTI devices are inexpensive and may be in the form of a label that can be attached or adhered to packages or objects. One advantage of TTI devices is that they can be quickly and easily visually inspected. A disadvantage of TTI devices is that the indicators may give false readings. False readings could result in the disposal or rejection of otherwise acceptable goods.
Electronic monitoring devices, such as data loggers, can be used to monitor and record a variety of different environmental parameters. Data loggers are small, battery-powered devices that may be equipped with a microprocessor, instruments, and a memory for storing data. Data loggers may be programmed to take specific measurements at desired time intervals. Data loggers can be used to create a more complete and accurate picture of any changes in environmental conditions. To retrieve the stored data, the data logger must be connected to a computer or reader that can retrieve and display the stored temperature readings. This may require additional time and labor to retrieve and analyze the data, and it may require additional equipment to process a larger number of data loggers. As a result, processing goods associated with electronic monitoring devices, such as a data logger, can be expensive, time-consuming, and inefficient. Some data loggers include LED displays that can digitally display temperature history. However, these data loggers are typically more expensive, and as a result, can be cost prohibitive. In addition, it may not be easy to quickly read an LED display because the electronic monitoring device could be disposed within a container or packaging envelope.
Thus, a need still exists to provide a method and apparatus for monitoring temperature exposure that can be performed rapidly and inexpensively, while at the same time maintaining accuracy.